Abstract: This study aims to systematically analyze the evolutionary characteristics and structural features of ecological and environmental protection policies in the Chishui River Basin, thereby revealing the policy logic and optimization pathways for collaborative governance in trans-provincial river basins. By collecting policy texts related to the Chishui River Basin over the years and employing quantitative analysis methods, an in-depth analysis is conducted from various dimensions, including policy intensity, issuing bodies, policy themes, and policy instruments . The research finds that policy formulation has undergone three stages: exploration (before 2012), piloting and experimentation (2012–2020), and collaborative governance (after 2020). The number and intensity of policies have consistently increased, demonstrating a process characterized by Guizhou taking the lead in pilot initiatives, the central government emphasizing and promoting efforts, and the provinces of Sichuan and Yunnan following up with responses. The issuing bodies form a diverse network involving collaboration among legislative, judicial, and administrative departments. Horizontally, legislative and judicial institutions dominate policy issuance, while vertically, government departments are the primary issuers, showing complementarity across different administrative levels. Policy themes and objectives have become increasingly diverse and systematic, which can be categorized into four types. At the central and provincial levels, the aim is to achieve cross-regional and cross-department coordination, whereas at the county/district level, the focus converges on expanding local interests. A variety of policy instruments are employed, but administrative mandate-based instruments absolutely dominate, with pre-event guidance instruments being the primary means. Economic incentive instruments and multi-stakeholder collaboration instruments are relatively underutilized. The provincial level serves as the main tier for designing policy instruments. This study recommends further strengthening inter-regional and inter-departmental coordination and cooperation, gradually improving the policy network to integrate ecological and environmental considerations with industrial and social development, innovating from the bottom up to design more monitoring, evaluation, and incentive-based policy tools, and enhancing policy implementation guarantees to achieve ecological prioritization and green development in the river basin.